The present invention relates to a video and voice signal processing apparatus that outputs an intelligible voice signal even if frame decimation is applied to a video signal when processing digital video and digital audio signals.
The invention also relates to a sound signal processing apparatus that reduces the amount of information in a digital sound signal.
Nowadays, encoding is often performed when transmitting or storing video signals and voice signals. Especially, in the case of video signals which carry enormous amounts of data, high-efficiency encoding (hereinafter called compression) is performed to reduce the amount of data, thereby reducing transmission or storage costs.
Encoded signals are subjected to decoding for reproduction; when the signals are in compressed form, expansion must also be performed. Generally, expansion often requires complex calculations, and in the case of moving images and the like which are to be processed in real time, high processing speed is needed.
There are, however, not a few cases where sufficient processing speeds cannot be obtained, for example, when performing processing by computer software. In such cases, appropriate decimation is applied to the input moving image signal to reduce the amount of data and to permit realtime processing.
One decimation technique frequently used is frame decimation. This technique decimates an input signal on a frame by frame basis when it is input.
A description will be given below of one example of a prior art video and voice signal processing apparatus in which an input moving image signal is first subjected to frame decimation and then to expansion and decoding, thus outputting a video signal and a voice signal. FIG. 7 is a block diagram showing the configuration of the prior art video and voice signal processing apparatus. In FIG. 7, 701 is a signal receiving circuit, 702 is a signal extraction circuit, 703 is a video signal processing circuit, 704 is a voice signal processing circuit, 705 is an input signal, 706 is an encoded video signal, 707 is an encoded voice signal, 708 is a video signal, and 709 is a voice signal.
FIG. 8 is an explanatory diagram showing individual frames of the input signal 705 arranged along the time axis. In FIG. 8, 801a and 802d are frames to be decoded, and 802b, 802c, 802e, and 802f are frames to be discarded by frame decimation.
The operation of the thus configured video and voice signal processing apparatus will be described. As an example, it is assumed here that two frames out of every three frames are discarded by frame decimation. In FIG. 7, the signal receiving circuit 701 receives the input signal 705, and supplies it to the signal extraction circuit 702. The signal extraction circuit 702 extracts signals corresponding to the frames 801a and 801d from the thus supplied input signal 705, separates the encoded video signal 706 and the encoded voice signal 707 from the extracted signals, and supplies them to the video signal processing circuit 703 and the voice signal processing circuit 704, respectively. At this time, signals corresponding to the frames 802b, 802c, 802e, and 802f of the input signal 705 are discarded. The video signal processing circuit 703 decodes the encoded video signal 706 thus supplied, and outputs the decoded signal as the video signal 708. Likewise, the voice signal processing circuit 704 decodes the encoded voice signal 707 thus supplied, and outputs the decoded signal as the voice signal 709.
However, in the above-described prior art configuration, not only the video signal but the voice signal is also decimated as a result of the frame decimation. Generally, when frame decimation is applied to a video signal, the video can still be recognized as a moving image though the motion becomes jerky; on the other hand, when frame decimation is applied to a voice signal, there occurs the problem that the voice can no longer be recognized as voice since signal continuity is lost.
The present invention has been devised in view of the frame decimation problem of the prior art, and an object of the invention is to provide a video and voice signal processing apparatus capable of outputting a voice signal recognizable as voice even when frame decimation is applied.
On the other hand, with the advance of digital signal technologies, sound is increasingly being recorded and reproduced using digital signals.
Nowadays, compact discs and minidiscs on which sound is recorded using digital sound signals are predominant as sound recording media for recording sound. In television broadcasting also, systems for transmitting both video and sound using digital signals are beginning to be employed, as seen in digital satellite broadcasting. Further, personal computers are increasingly used for sound processing such as recording or reproduction using digital sound signals; nowadays, with improvements in the performance of personal computers, it is not uncommon for personal computers to reproduce video and sound simultaneously by using digital signals.
As shown in FIG. 9, a prior art sound signal processing apparatus 1 is an apparatus that accepts at its input a reproduced sound signal A of a digital sound signal transmitted from a sound signal transmitting apparatus 2, and that converts it into an analog sound signal and outputs the analog sound signal as an output sound signal B.
In recent years, advances have been made in sound quality and sound multiplexing in stereo broadcasting or the like, and the reproduced sound signal A from the sound signal transmitting apparatus 2 may contain a large amount of information.
However, since the above prior art sound signal processing apparatus 1 converts the reproduced sound signal A into an analog sound signal in the order in which it is input, if the reproduced sound signal A is a signal containing a large amount of information, problems will occur, such as interruptions in the sound corresponding to the reproduced sound signal A, unless the speed with which the sound signal processing apparatus 1 converts the reproduced sound signal A into the analog output sound signal B is fast enough.
A first aspect of the present invention concerns a video and voice signal processing apparatus which comprises: signal receiving means for receiving an input signal containing an encoded video signal and an encoded voice signal, and for recovering from the input signal the encoded video signal and encoded voice signal for output; video signal extracting means for extracting a designated frame from the encoded video signal, and for outputting the extracted frame as a representative video signal; video signal processing means for applying prescribed processing to the representative video signal, and for outputting the thus processed signal as a video signal; and voice signal processing means for applying prescribed processing to the encoded voice signal, and for outputting the thus processed signal as a voice signal.
In this configuration, frame decimation is applied to the encoded video signal, but is not applied to the encoded voice signal; therefore, all voice signals can be output unchanged.
This invention also provides a video and voice signal processing apparatus which comprises: signal receiving means for receiving an input signal containing an encoded video signal and an encoded voice signal, and for recovering from the input signal the encoded video signal and encoded voice signal for output; video signal extracting means for extracting a designated frame from the encoded video signal, and for outputting the extracted frame as a representative video signal; video signal processing means for applying prescribed processing to the representative video signal, and for outputting the thus processed signal as a video signal; voice signal extracting means for extracting designated information frame by frame from the encoded voice signal, and for outputting the extracted information as a representative voice signal; and voice signal processing means for applying prescribed processing to the representative voice signal, and for outputting the thus processed signal as a voice signal.
In this configuration, since only representative information is extracted from every frame of the encoded voice signal, sound quality degrades but an uninterrupted and intelligible voice signal can be output.
A second aspect of the present invention considers the problem of the earlier described prior art sound signal processing apparatus, that is, the slow speed in converting a digital sound signal containing a large amount of information into an analog sound signal, and thus provides a sound signal processing apparatus that converts a digital sound signal containing a large amount of information into an analog sound signal at high speed.
This invention provides a sound signal processing apparatus which comprises: extracting means for taking as an input a composite digital sound signal representing digitally a plurality of sounds that are related to each other, and for extracting from the composite digital sound signal a digital sound signal corresponding to one or more of the sounds; and signal converting means for converting the digital sound signal extracted by the extracting means into an analog sound signal.
This invention also provides a sound signal processing apparatus which comprises: averaging means for taking as an input a digital sound signal representing a plurality of sounds that are related to each other, each sound being represented by a prescribed number of samples, and for averaging digital values of signals sampled at the same sampling instant between digital sound signals corresponding to two or more sounds arbitrarily selected from among the plurality of sounds; signal converting means for converting the averaged digital sound signals and/or unaveraged digital sound signals into analog sound signals.
This invention further provides a sound signal processing apparatus which comprises: bit count reducing means for taking as an input a digital sound signal sampled, quantized, and expressed by k bits, and for extracting high-order j bits (k greater than j) of the k bits of the digital sound signal; and signal converting means for converting a digital sound signal consisting of the j bits extracted by the bit count reducing means into an analog sound signal while considering the j bits are high-order bits of the k-bit digital sound signal.
This invention also provides a sound signal processing apparatus which comprises: sample deleting means for taking as an input a digital sound signal consisting of a prescribed number of samples, and for deleting samples from the digital sound signal with a prescribed periodicity; and signal converting means for converting digital sound signals left undeleted by the sample deleting means into analog sound signals.